Audio frequency coupling



June 2, 1931. I H. P. DONLE 1,808,726

AUDIO FREQUENCY COUPLING Filed May 9. 1928 Patented June 2, 1931 y UNITE STA HAROLD?. DONDE, or MRInnm CONNECTICUT, Assignee., BY MESNE ASSIGNMENTS, 'ro RADIO INVEN'rIoNs,y INC., A CORPORATION or NEW YORK Aunido 'FREQUENCY `Cotrmliir Application aleaMay e, Y192s. `serial No. 276,346.

invention relates particularly to multistage vacuum tube amplification systems.

The main object is to provide apparatus for coupling tubes to produce a maximum amplification throughout a wide range of frequencies and without distortion.

Another object is to provide a compact device which will have as high a degree of eficiency as possible for a minimum cost of construction.V

V A specific object is to utilize the magnetic core to a maximum degree. Y

I accordingly utilize a combination of impedance and auto transformer coupling with all of the coils mounted on a single closed magnetic core having a cross bar. The choke coil is formed of two similar parts mounted on opposite ends of the core and so connected that the lines of force in the cross bar are substantially balanced and the transformer is mounted on the cross bar so as to utilize the same magnetic core without being coupled to the choke coil. A condenser is inserted between the plate circuit of the first tube and the transformer at a point to provide a step-up ratio of say lrto 7 or 8.

Fig. l shows one form of coupling device embodying my invention.

Fig. 2 shows one form of circuit with cou tpl-ing devices according to my invention.

In F ig. l I have illustrated the coupling between two vacuum tubes 5 and 6 which may be of any suitable type. The inductive part of the coupling device includes the coils 7, 8, 9 and l0 and the capacitative part Vincludes the condenser 1l. The coils 7 and 8 constitute two substantially equal choke coils inserted in the plate circuit of the lirst tube. The coils 9 and 10 constitute two sections of an auto transformer which is connected in the grid circuit of the second tube. The condenser 11 is connected to a point between the coill sections 9 and 10 and to the plate circuit of the first tube.

tions 9 and 10 are mounted on the central j The coils are all mounted on a core l2VV crossbar 15 of thecore. 'Ilie'coil s'e`ctions`7 and 8 are so wound and connectedthat the magneticfiux produced bythem inthe `central cross bar l5 is inopposite directionsso that in effect the central cross bar is neutral so far themag'netic effect of the coils 7 and 8 isconcerned. The heavy arrows indicate thedirection of the lines o'fforce produced fby thedirect current in the' choke sections; i y

` The ldotted arrows indicate thedire'c'tion fo" ofthe lines of force produced by the alternan' i.

ing current in the transformer;

AAlthough the proportions and values Aof the various components of this coupling sys# temmay be yvaried considerablyIhave'found l satisfactory results may be attained by using a magnetic'core the cross section of thend and sidebars of fwhich is say"1/` square.'

The choke coil sections maye'aohfconsistofr six'thousa'ndturns andthe aut'o transformer coil sections mayconsist respectively of three thousand turns and twenty thousand turns:`

A suitable condenser may hav-'ea capacity off say .02 mf. It shouldbe understoodhowever that I -do "not consider the invention as limited to' these spcifie values. Y

In the 'diagram of F 2"I have i'llas-` trated theinventi'on' as applied totwofstafges of audio frequency coupling. .In this'diar gram I have lal'solillustrated abiasigor'C battery for the grid of'the'f-tubef I also"V wishitlto be understdo'dthat theAj-ad'B" batteries illustrated 4are merely l"s ymbolicf any'suitable fsolurcejof current supply.

If the effectof the 'chokecols 7 and' S-i'snot lbalancedas above set forth there willb'e'a residual; magneti@ dieet-upon the' auttransformer whichwill affect its ratio. Y v

By varyingthe' capacity couplingfforf the variousstages each may beadjust'ed "to *a maximum sensitivity. l V

The step-up ratio vforthe variou's"stages g may differ if desired. f

Iolaim:

1. An audio frequencycoupling device hav'- ing 'capacitativ'eand inductiveelements forfa vacuum tubjeampli-en thelatter consisting of a closed'iron core having! a central `leg and' two outer legs5 Awindings upon said outer legs connected in series,. said windings being lso um.V

- directioned as to cause their magnetic paths l I n n two `choke windings for supplying direct cur-- vto include substantially only the periphery of the core and serving to feed plate potential to the plate of the previous tube and a step-up auto transformer having windings carried by said central leg the input to said auto transformer being through said capacity element and having its output connected to the succeeding vacuum tube.

' 2. An audio frequency coupling deviceH comprising-a closed ferrousvcore having' end .bars andan intermediate bar, substantially equivalent windings mounted on Ythe Vend bars, an auto transformer coil mounted on the intermediate baranda condenser coupling between the windings on the end bars v and the input to the transformer,` the ratio of i the two parts of the auto transformer being between lto 7 and 1 to-S. y

3. An intertube coupling ,device having rent to the plate of a preceding tube and an ings together with a capacitative coupling connected between one end of the choke and at a point intermediate the ends of the transformer winding such that the step-'up ratio l to 7.67. .p HAROLD DONLE.

is approximately auto transformer `winding for transferring having a common magnetic core,-the choke l winding being divided intotwo substantially and stepping-up the alternating voltage from the plate circuit of the preceding tube to the grid circuitV of the following tube, said windings being carried-upon a single ferrous core and said'windings being so d'irectioned that substantially no coupling exists betweenthe direct land alternating current windings, and

capacity inserted between.A the plate of the V first'tube andthe input to the .auto transformer which supplies alternating current to thejfollowing tube.-

g n 4;. A coupling device comprising two oppositely disposed choke coils adapted ,to be connected in series between the plate of one tube and the plate power supply, anzauto l transformer having' its inputl terminals connected in series with a condenser between the f plate of thefirst tube and the filaments and having its output terminals connected between the lament and the grid of the next Y tube 'andla singlecore structure for the choke and transformer coilsso constructed and arranged that there are no substantial common iiux linkages or energy transfer-between the choke coils and the auto transformer.

5. An audio frequency coupling device comprising vra closed core.;4 having end and -intermediate bars with substantially equaly chokecoils on the end bars and an auto transformer coil on the intermediate bartogether vwith ay capacitative coupling between the vchoke coils and the transformer coil.

6. A multi-stage audio, frequency amplifiersystem including relay elements and inductive and capacitative coupling between said elements said inductive couplingcomprising V,choke and autoy transformer coils equal parts and the transformer winding being divided into two unequal parts the Y capacitative coupling being connectedV at one 

